Ni-Cd batteries are often used in the aircraft industry. They have many advantages for aircraft applications. There is, however, some difficulty in charging Ni-Cd batteries. They cannot be tested by reading the specific gravity. The beginning point is hard to determine. In charging them, the beginning point is usually an initial partial charge. Usually, it is not possible to measure the precise amount of charge already in the battery. The size of the charge in the battery limits the additional amount of charge permitted. Battery size limits or determines the rate at which additional charge can be forced into the battery. Surprisingly, it has been discovered that it is better to initially discharge a Ni-Cd battery to some minimal level. Thereafter, it is charged for a stated interval. The charging rate is high for this interval. The charging rate during charging is constant; it is, however, preferable to charge with periodic interruptions. It has been found that the chemical reactions within the battery required to produce the charging reaction are aided by these periodic interruptions. These interruptions are superimposed on the existing analog charge signal with both rate and duty cycle of these interruptions being adjustable. Once about 90% of the full charge is placed in the battery, the rate is cut by about 75% to 90% to top off the charge. Eventually, the battery is charged to a level determined by elapsed time and charging rate and when this is accomplished, the battery is then ready for use.
The present invention is a device which charges Ni-Cd batteries without regard to their initial charge level by first discharging the battery. Moreover, it is able to charge a single battery or multiple batteries repeated numbers of times without limitations on its operation. The functioning of the device will become more apparent upon a description of the device which follows.